Do you mean Visual Basic for Applications? How are you creating a GUI in Excel?

Mostly just locking fields. I don’t do anything procedural. It’s usually calculators, stats and modelling stuff.

I think there is a thing called Microsoft Office development kit or some other name that allows C# and other .Net programs to manipulate Office apps. Not sure if it's what the author meant, though.

Oh, I have used OLE (or some iteration thereof) to drive Excel from Python. That was a long time ago, but it sounds similar. I wasn't really doing GUI, though - I was using code to build spreadsheets from data files.

I had something I wrote in the 90s I wasn't proud of that was a word macro that read Excel sheets for a list of instructions and used those to compose documents and print them. I feel sick thinking about it.

Reminds me of Moe on the Simpsons saying I've done things I'm not proud of. And the things I am proud of are disgusting.

You should be proud like that.

I remember using Office Interop back in the day

Less useful these days as we use open formats, ie doc is propriatery, docx is open